A light-emitting device, such as a light-emitting diode or a laser diode, using a group III-V or II-VI compound semiconductor material is capable of emitting various colors, such as red, green, blue, and ultraviolet light, as the result of advances in thin film growth technology and materials for the device. In addition, the light-emitting device may emit white light with high efficiency using a phosphor or by combining colors. Furthermore, the light-emitting device has advantages of lower power consumption, a semi-permanent lifespan, a rapid response time, good safety, and environmental friendliness, when compared to conventional light sources, such as a fluorescent lamp and an incandescent lamp.
White light may be obtained using a single-chip module, in which a phosphor is coupled to a blue or ultraviolet (UV) light-emitting diode chip, or using a multi-chip module including a plurality of chips.
In the multi-chip module, three kinds of chips, namely red, green, and blue (RGB) chips, are combined to obtain white light. In the multi-chip module, however, color coordinates may be changed due to the non-uniformity in operating voltage between the chips or the difference in output between the chips caused by the surroundings.
In the single-chip module, a Y3Al5O12:Ce3+ (YAG:Ce) phosphor is excited by light emitted by a blue light-emitting diode (LED) to obtain white light. In the case in which the YAG:Ce phosphor is used, however, it is difficult to control a color temperature and a color rendering index (CRI).